1. Field of the Invention
The invention relates to an integrated circuit having a plurality of output drivers which are supplied with a supply voltage via a plurality of supply terminals.
2. Description of the Related Art
Integrated circuits have output drivers to drive internally generated signals toward the outside. Particularly in the case of simultaneously switching output drivers, line disturbances are generated in the form of interference signals, which can have a considerable effect on the signal processing and on other signal lines. The line disturbances are spread in particular by the inductive properties of the interconnects or capacitive coupling effects since adjacent interconnects or interconnects in proximity are thereby influenced. The line disturbances may be taken up for example by the interconnects of the integrated circuit, the housing terminals and their connections, the conductor tracks on the printed circuit board and the like and influence circuits connected thereto. The rapidity of the alternation of currents which flow through the interconnect generates differential voltage fluctuations which influence the signal integrity. These line disturbances may influence the distribution of the supply voltages VDD and VSS, inter alia.
In particular, these line disturbances are observed in integrated circuits having simultaneously switching output drivers. In the case of DRAM memory circuits, the supply and ground lines are in each case produced in the form of a simple homogeneous metal interconnect having suitable connecting lines to the respective output driver circuits. DDR-DRAM circuits have, for example, eighteen (18) such connecting line pairs which in each case connect the high supply voltage VDD and ground to the respective output driver.
On account of the length of the supply interconnects, which may amount to as much as half the chip length, line disturbances may be transmitted over the entire length of the interconnects. This may bring about signal disturbances in other regions of the integrated circuit.
RC filters are customarily used to attenuate the line disturbances on the supply voltage lines. However, an RC filter includes a capacitance which requires a comparatively large area in the case of a realization in an integrated circuit. Moreover, the metal interconnect representing the resistance portion of the RC filter may have an excessively large resistance which results in an unmatched RC time constant.